Device for discriminating between fixed and moving objects



March 2, 1948.

R. E. RUTHERFORD 2,437,173

DEVICE FOR DISCRIMINATING BETWEEN FIXED AND MOVING OBJECTS Filed July 27, 1945 Patented Mar. 2, 1 948 DEVICE FOR DISCRIMINATING BETWEEN. FIXED AND MOVING OBJECTS Robert E. Rutherford, Nutley, N. J., assignor to Allen B. Du Mont Laboratories, Inc., Passaic, N. J., a corporation of Delaware Application July 27. 1945, Serial No. 607,355 (01. 315-9) 13 Claims.

This invention relates to a device for receiving a reflected signal from either stationary or mov-, able objects. The device may be mounted upon a stationary or moving support.

In carrying out the invention an electron tube is provided by means of which a. signal is produced that is synchronized with in image signal, and provision is made for controlling the produced signal so that it may neutralize the image signal. Provision is made so that there may be a time delay in producing the neutralizing signal so that the image signal appears upon a screen a short interval of time before it is erased or neutralized. The two signals may be first combined so that only the diiferences between the resulting signals appear on the image tube. The time and intensity of the neutralizing signal can be controlled so as to produce a wide variety of results. The erasing signal is applied to the the image tube in such way that it is always in the exact location on the image tube for producing the desired efiect or the proper erasing.

By this invention means are provided by which the danger of burning the screens of such cathode-ray tubes is greatly reduced or entirely eliminated. This invention is particularly usefill in connection with tubes that have screens of the dark trace type. Also, with this invention signals from moving objects can be observed in places where fixed objects are present without being obscured by signals from said fixed objects.

In carrying out the invention, an auxiliarv cathode-ray tube is used to generate an erasing signal which will cancel or reduce the signal on the dark trace tube, on which the signal is recorded.

Amplifiers are provided and arranged so that adjustments may be so made that reflections from fixed positions can be erased from the screen and reflections from moving'objects appear in full contrast.

The invention may be understood from the description in connection with the accompanying drawing, in which:

Fig. 1 is a diagram of connections for carrying out the invention;

Fig. 2 shows a modification of some of the parts: and

Fig. 3-shows another modification of some of the parts.

In the drawing, reference character I indicates a cathode-ray tube that is provided with means 2 referred to as a cathode-ray gun to produce a cathode-ray beam and cause it to scan an electron storage surface. This storage surface may,

2 for example, be a metallized surface 3 formed into a mosaic, as indicated in Fig. 1. The tube I is provided with a signal collector 5 which is provided with a lead 6 extending to the outside of the tube I and being hermetically sealed through the wall thereof.

A diflerent cathode-ray tube 1 is provided with a screen 8 which is white and of such a character that the trace of the cathode-ray beam from the gun 9 thereon is dark and varies in intensity with the strength of this beam.

A scanning generator shown diagrammatically at I is provided for applying the horizontal and vertical, deflecting signals to the deflecting plates of the tubes I and I. An amplifier I I is provided for amplifying the signal from collector to the cathode I 2 of tube 1, this cathode being returned to ground through resistor I3.

' Lead l5 extends from the receiver I6 for the reflected signal'to amplifier II from which leads I8 and I9 extend to the control grids and 2|. respectively, of the tubes I and I. The grid 20 is biased to cut-off in any convenient way.

In the modification shown in Fig. 2 the face of 26 the tube I is a dielectric which forms the storage surface 3' for the electrons. The signals are collected from this surface by a metal coating or plate 25 which covers the signal area. The signals are applied by lead 26 to the amplifier II shown in Fig. 1. No collector ring is needed in this modification. The other parts are the same as in Fig. 1, and the operation is as described above in connection with Fig. 1.

In the modification shown in Fig. 3, a mosaic 3" is applied to the inside surface of the end of the tube I" and a metal plate 25' is applied to the outer end of this tube and the signals are applied by lead 26 as described in connection with Fig. 2.

Theoperation is as follows:

The gun of cathode-ray tube I forms a beam of electrons which is caused to scan the storage surface 3 and the cathode-ray gun of tube I causes its beam to scan the screen 8 in synchronism with the beam of tube I since the scanning of both beams is caused by the same scanning generator In The incoming reflected signal after being amplified by amplifier I1 is fed to the control grids 20 and 2| of tubes l and 1, the grid 20 being normally biased to cut-off. The incoming signal which is applied to grid 20 causes an electron flow to the storage surface 3 of tube I, thus charging an area thereof during theperlod of scanning by the beam, the area being retraced once during each scanning periodwhich is determined by the frequency of the scanning generator III. This chargesthe surface 3 to suchan extent that electrons soon begin to pass to the collecting ring 5 and thence to the amplifier II from which the amplified signal passes to the cathode I: of the dark trace tube 1. The phase of the signal from the tube I which is applied to the cathode i2 is of the same polarity as that applied to the grid 2| of this tube and its amplitude is so adjusted that it is equal to the amplitude of the signal that is applied to the control grid 2| by lead l9, so that the signal on the screen of tube I is cancelled when desired.

In this way all signals from fixed objects are cancelled so that permanent burning of the screen by signals from such objects is obviated. The beam current of tube I or the gain of the signal from collector 5 or both may be so adjusted that the signal from it which is applied to the cathode of tube I will cause any desired intensity of the trace on screen 8 so that the trace will be easily visible without burning the screen or very light so that it may be detected or it may be eliminated entirely. Also, by the same sort of adjustment of amplifier II the fixed objects may be made to appear lighter on the screen 8 than the moving objects or targets which may be made darker than normal.

It will also be obvious that during and shortly after a change of range of this device, reflected signals both from stationary and moving targets will appear on the screen 8. It requires several repetitions of scanning to extinguish signals reflected from stationary objects, due to electrons passing from mosaic 3 to collector 5.

By this invention the danger of burning the white screen upon which the signals are received is eliminated; the time of decay of signals from fixed objects can be controlled; the contrast between signals from fixed and moving objects can be regulated; the device is not complicated, and its operation is easily controlled.

What is claimed is:

1. In a device of the character described, a cathode-ray tube having a screen, a cathode-ray tube having its control grid in parallel with the control grid of said first named tube and having a storage dielectric, and means to apply a signal from said second named tube toa beam intensity controlling electrode of the gun structure of said first named tube.

2. The device of claim 1, in which means are also provided to apply a signal to corresponding beam intensity controlling electrodes of said tubes.

3. The device of claim 1, in which means are provided toapply a signal to the control grids of said tubes.

' 4. The device of claim 1, in which means are provided to amplify the signal from said second named tube.

5. The device of claim 1,- in which the scanning signals for said tubes are from the same source.

6. A cathode-ray tube having a screen upon which a. moving cathode-ray produces a visible pattern, a cathode-ray tube having a storage surface, means to apply a common signal to corresponding beam intensity controlling electrodes of, said tubes, and means to apply a signal from said storage surface to a beam intensitycontrolling electrode of the other tube.

7.The device of claim 6, in which said last mentioned electrode is the cathode.

8. The device of claim 6, in which said corresponding electrodes are control grids.

9. The device of claim 6, in which means are provided to amplify the signal from said storage surface before it is applied to said beam intensity controlling electrode of the other tube.

10. The device of claim 6, in which said storage surface is a dielectric whose surface has metal particles applied thereto.

11. The device of claim 6, in which said storage surface is a dielectric. v

12. A device of the character described comprising a cathode-ray tube having a cathode, a control grid, deflecting means and a screen, a second cathode-ray tube having a cathode, a control grid, deflecting means and a storage dielectric, said second named tube having the control grid thereof connected in parallel with the control grid of said first named tube, and means to apply a signal from said second named tube to a beam intensity controlling electrode of said first named tube.

13. The device of claim 12, in which means are also provided to apply a signal to corresponding electrodes of said tubes.

ROBERT E. RUTHERFORD.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

